This invention relates to a loudspeaker for audio and video applications, and more particularly, to a loudspeaker having an improved air cooling system.
Loudspeakers, or speakers, are well known in the art and are commonly used in a variety of applications, such as in home theater stereo systems, car audio systems, indoor and outdoor concert halls, and the like. A loudspeaker typically includes an acoustic transducer comprised of an electromechanical device which converts an electrical signal into acoustical energy in the form of sound waves and an enclosure for directing the sound waves produced upon application of the electrical signal.
A loudspeaker comprises a coil of wire, typically referred to as a voice coil, which is suspended between a pole piece and a permanent magnet. In operation, an alternating current from an amplifier flows through the voice coil which produces a changing magnetic field around the voice coil. The changing magnetic field around the voice coil interacts with the magnetic field produced by the permanent magnet to produce reciprocal forces on the voice coil representing the current in the voice coil.
The voice coil is disposed within the loudspeaker so that it can oscillate in accordance with the reciprocal forces along the pole piece. The voice coil is attached to a cone shaped diaphragm which vibrates in response to the oscillation (reciprocal movement) of the voice coil. The vibration of the diaphragm produces acoustic energy in the air, i.e., a sound wave.
The voice coil is constructed of a conductive material having electrical resistance. As a consequence, when an electrical signal is supplied to the voice coil, the electric current flowing through the coil generates heat because of the interaction with the resistance. Therefore, the temperature within the loudspeaker and its enclosure will increase. This resistance in the voice coil to the current flow represents a significant part of the loudspeaker""s impedance, and a substantial portion of the electrical input power is converted into heat rather than into acoustic energy.
Such temperature rise in the voice coil creates various disadvantages. As an example of disadvantage, it has been found that significant temperature rise increases the resistance of the voice coil. This, in turn, results in a substantial portion of the input power of the loudspeaker to be converted to the heat, thereby lowering the efficiency and performance of the loudspeaker. In particular, it has been found that increased resistance of the voice coil in the loudspeaker can lead to non-linear loudness compression effects at high sound levels.
When additional power is supplied to compensate for the increased resistance, additional heat is produced, again causes an increase in the resistance of the voice coil. At some point, any additional power input will be converted mostly into heat rather than acoustic output. Further, significant temperature rise can melt bonding materials in the voice coil or burn out the voice coil, resulting in permanent structural damage to the loudspeaker.
Various methods have been applied to both loudspeakers and speaker systems to improve heat dissipation, including improved conduction and convection techniques, venting, and the use of forced air cooling with fan-type devices. However, no adequate, practical and affordable solution has been found to maintain desirable operating temperatures under high power conditions.
For example, in U.S. Pat. No. 5,357,586, there is disclosed a flow-through air-cooled loudspeaker system. The loudspeaker and the enclosure are provided with air passages which are aerodynamically-shaped. The air passages provide low-pressure regions for inducing flows of air into and about the driver motor of the loudspeaker in response to the vibratory movement of the speaker diaphragm. Further, an aerodynamically-shaped body is disposed within the pole piece to define a ventilation passage for exchange of air between an interior chamber defined by a coil former and the back of the speaker.
Aerodynamically-shaped openings are provided through the pole piece for inducing flow of air about the voice coil in the voice coil gap between the pole piece and permanent magnet. The speaker frame support is provided with aerodynamically-shaped openings to induce air flow into the interior chamber. In this manner, low-pressure regions established by the aerodynamic shapes induce flow of cooling air about the voice coil and pole piece in response to vibratory movement of the cone. Aerodynamic shapes are disposed in the intake and exhaust vents of the speaker enclosure to exchange air between the enclosure and atmosphere in response to vibratory movement of the speaker diaphragm.
The loudspeaker system in U.S. Pat. No. 5,357,586 has drawbacks. For example, to establish the air passages, the voice coil former has a plurality of apertures or openings circumferentially spaced thereabout. Such apertures play a role of additional resistance against reciprocal movement of the voice coil former or the vibration of the diaphragm. Thus, such a structure having apertures on the voice coil former degrades the sound quality of the loudspeaker and may also weaken the voice coil structure.
Other methods such as cooling fans and pressurized air have been used in both loudspeakers and speaker systems, but are cumbersome, unreliable and expensive. The methods that employ electrical motors which draw from the electrical audio signal cause an unacceptable decrease in system efficiency.
It is, therefore, an object of the present invention to provide a loudspeaker having an improved cooling system which is free from the problems associated with the conventional loudspeaker cooling system.
It is another object of the present invention to provide a loudspeaker having an improved cooling system which utilizes air flow to prevent significant temperature rise in the voice coil.
It is a further object of the present invention to provide a loudspeaker having an improved cooling system which produces air flows to prevent significant temperature rise in the voice coil through the vibration of the speaker diaphragm during normal operation.
It is a further object of the present invention to provide a loudspeaker having an improved cooling system in which a heat transfer plate is separately formed from the speaker frame, thereby simplifying the design and decreasing the overall cost of the loudspeaker.
It is a further object of the present invention to provide a loudspeaker having an improved cooling system in which a heat transfer plate is structured to prevent unwanted particles from coming in the loudspeaker when ventilating the air.
Accordingly, a loudspeaker of the present invention is comprised of a speaker frame, a diaphragm connected to the speaker frame in a manner capable of vibration, a voice coil which is formed on a voice coil bobbin and is connected to the diaphragm for vibrating the diaphragm, a permanent magnet having a central opening, a pole piece disposed coaxially within the central opening of the permanent magnet to form an air gap between the pole piece and the permanent magnet into which the voice coil is disposed, and a heat transfer plate made of non-magnetic and thermal conductive material and disposed over the permanent magnet.
The heat transfer plate has a plurality of cooling fins which are radially outwardly extending toward an outer rim thereof and inner and outer air openings on the outer rim. The heat transfer plate forms air passages each having an air path formed between two adjacent cooling fins and said inner and outer air openings. The vibration of the diaphragm produces air flows through the air passages to intake cool air and exhaust heated air between the inside and outside of the loudspeaker.
The cooling fin is inclined in a manner to increase its height toward the outer rim, and the outer rim has a step like shape in cross section and has a flat upper surface which is higher than top ends of the cooling fins. The heat transfer plate has a floor which is inclined toward the outer rim in a degree smaller than that of the cooling fins, the air path which is a channel defined by two adjacent cooling fins is continuous to said inner air openings provided at an inside wall of the outer rim while the outer air openings are provided at an outside wall of the outer rim.
The inner air opening and said outer air opening formed at the outer rim have different positions relative to an axial direction of the loudspeaker from one another. The inner air opening has a wall and the outer air opening has a projection to bend the air passage between the inner air opening and the outer air opening, thereby preventing unwanted particles from coming inside of said loudspeaker.
The pole piece has an axial opening to establish an axial air passage between the inner area of the voice coil bobbin and the outside of the loudspeaker. The vibration of the diaphragm produces air flows through the axial air passages to intake cool air and exhaust heated air between the inside and outside of the loudspeaker.
According to the present invention, the loudspeaker has an improved air cooling system which utilizes air flow to prevent significant temperature rise in the voice coil. The air cooling system produces air flows to prevent significant temperature rise in the voice coil through the vibration of the speaker diaphragm during the normal operation.
In the loudspeaker of the present invention, the heat transfer plate is separately formed from the speaker frame, thereby simplifying the design and decreasing the overall cost of the loudspeaker. Further, the heat transfer plate is structured to prevent unwanted particles from coming in the loudspeaker when ventilating the air, which maintains the performance level of the loudspeaker.